The invention relates to a driving arrangement for a drive motor with which at least one current controller is associated. The current controller controls semiconductor switching elements of an electronic power stage associated with the drive motor in dependence on a rotor position transmitter coupled to the rotor of the drive motor.
Such a driving arrangement is known from DE-OS No. 31 20 559. In such driving arrangements, a wavy course of the torque is obtained because of the shape of the B-field curve. A breakdown of the torque occurs at every commutation process.
It is an object of the present invention to develop a driving arrangement of the type described at the outset in such a manner that the breakdown of the torque is substantially reduced to thereby decrease torque ripple.
According to the invention, the stated problem can be solved by providing a number of auxiliary windings corresponding to the number of phases of the drive motor. The auxiliary windings are associated with a magnetically excited rotor, the pole position of which agrees with the rotor position transmitter. The auxiliary windings are arranged at a physical spacing of 360.degree./2 pm relative to one another, where p corresponds to the number of pole pairs of the drive motor and m corresponds to the number of phases of the drive motor. The auxiliary voltage induced in the auxiliary winding is superimposed after rectification to the current reference value as a supplementary reference value. Due to the described arrangement of the auxiliary windings, a non-sinusoidal auxiliary voltage is induced therein which has a pronounced maximum at each commutation instant. Due to the fact that this auxiliary voltage is superimposed on the current reference value, the current reference value has, at every commutation instant, a value which is increased by an amount corresponding to the maximum of the auxiliary voltage occurring at that instant. Accordingly, the load current of the drive motor is controlled-upwardly according to the course of the current reference value at the instant of commutation.
A further solution of the problem comprises, in a driving arrangement, in which a tachometer generator is connected to the motor rotor. The tachometer generator comprises a multiphase stator winding of which the number of phases corresponds to the number of phases of the drive motor and is designed so that in each phase of the stator winding, a voltage which is constant at least over a given angular range is induced and the angular regions in which the individual phase voltages change from one polarity to the other do not overlap in time. The individual phase voltages are added up by means of a summing stage to form an auxiliary voltage which is subtracted amplitude-wise from the current reference value of the current controller. Due to the described course of the phase voltages of the tachometer generator, an auxiliary voltage is obtained by adding them up which has a pronounced minimum at each commutation instant. Due to the fact that this auxiliary voltage is subtracted as far as the magnitude is concerned, from the current reference value, the current reference value has at every commutation instant an increased value according to the minimum of the auxiliary voltage occurring at this instant, so that also in this case, the load current of the drive motor is controlled-upwardly according to the course of the current reference value at the instant of commutation.
In both solutions, the torque breakdown caused by the drop of the field curve in the commutation region by the load current, which is larger at the commutation instant, is reduced substantially so that the torque ripple is decreased.
Due to the fact that the auxiliary windings are arranged in the stator of the drive motor and are induced by the rotor field of the drive motor, a separate machine unit for generating the auxiliary voltage become unnecessary. In a driving arrangement with a speed control superimposed on the current controller, a tachometer generator coupled to the drive motor is required for setting the actual speed value. In this case, the auxiliary windings can be arranged in the stator of the tachometer generator and can be induced by the rotor field of the tachometer generator.
Since a number of auxiliary windings corresponding to the number of phases of the drive motor is provided and the auxiliary voltage must be rectified, a correspondingly large amount of rectifier elements results. This cost can be reduced by connecting all auxiliary windings in series. By this series connection of the auxiliary windings, a single auxiliary voltage is obtained, the frequency of which is a multiple corresponding to the number of the auxiliary windings of the frequency of an individual auxiliary winding. Thus, also this single auxiliary winding has a maximum at every commutation instant, by which the current reference value is then increased accordingly. Since only a single auxiliary voltage still need to be rectified, the amount of rectifier elements and also of control lines, is reduced.
The magnitude of the voltage induced in the auxiliary windings is proportional to the speed of rotation of the drive motor or of the tachometer generator coupled thereto. For raising the current reference value, however, a value as constant as possible is required. A constant value of the auxiliary voltage which is independent of speed variations and which is to be superimposed on the current reference value is achieved by the provision that the auxiliary voltage furnished by the tachometer generator is matched as to its amplitude to the level of the actual speed value and both voltages are fed to the inputs of a divider stage in such a manner that the auxiliary voltage is divided by the actual speed value voltage. Furthermore the output of the divider stage is connected to one input of a multiplier stage, at the other input of which the current reference value is present and the output of which is connected to a comparator stage which precedes the current controller and carries out the reference/actual value comparison.
The matching of the auxiliary voltage to the magnitude of the actual speed value voltage can be accomplished by designing the auxiliary windings in such a manner that the crest value of the auxiliary voltage is approximately equal to the level of the actual speed voltage or also by feeding the auxiliary voltage to the divider stage via a normalizing stage.
By the normalizing stage, the value of the auxiliary voltage is matched to the value of the actual speed voltage. By matching the voltage maximum of the auxiliary voltage to the level of the actual speed value voltage and the formation of the quotient of the two voltages a constant control variable independent of the absolute magnitude of these voltages is obtained at the instant of the voltage maximum of the auxiliary voltage. Thereby, the current reference value is always increased by the same value in the commutation region, independent of the speed.
Due to the fact that in a driving arrangement with a three-phase drive motor, the angular range in which the individual phase voltages of the tachometer generator are constant, extends over 120.degree., a triangular waveshape of the auxiliary voltage is obtained, the amplitude of which corresponds to the amplitude of the individual phase voltages. By means of a curve generator, the shape of the auxiliary voltage can be adapted to the existing conditions.
A constant value, independent of speed variations, of the auxiliary voltage to be superimposed on the voltage reference value is achieved by the provision that the magnitude of the auxiliary voltage and the actual speed voltage formed by the tachometer generator are fed to the inputs of a divider stage in such a manner that the magnitude of the auxiliary voltage is divided by the actual speed value voltage; and that further, the output of the divider stage is connected to one input of a multiplier stage, to the other input of which the current reference value is applied and the output of which is connected to a comparator which precedes that current controller and carries out the reference value/actual value comparison.
Referring to an exemplary embodiment shown in the drawing, the subject of the application will be described in greater detail.